This invention relates to retrofocus type objectives of long back focal length suited for use in single lens reflex cameras, and more particularly to retrofocus type wide angle objectives of minimized bulk and size.
The retrofocus type objective, because of its intent of lengthening the back focal length, uses a negative lens of strong power at the front. This produces the drawback of increasing the distortion, coma, halo of sagittal rays, and other abberrations. To minimize the bulk and size of the objective as in the present invention, the negative power of the front component is required to be stronger than that of the ordinary retrofocus type objective. Thus, the various aberrations tend to increase further. Particularly with an objective of large relative aperture, the halo of sagittal rays becomes serious, and good correction of the aberrations becomes difficult.
A wide variaty of retrofocus type objectives have already been developed. Examples of an objective comprising a negative front group, a positive middle group, a diaphragm, and a positive rear group, the front group including negative, positive and negative lenses, and the rear group including negative, positive, positive lenses, are shown in U.S. Pat. No. 3,736,049 and No. 3,982,823.